Memory Error Detection

ABSTRACT

Systems and methods are provided for detecting and correcting address errors in a memory system. In the memory system, a memory device generates an error-detection code based on an address transmitted via an address bus and transmits the error-detection code to a memory controller. The memory controller transmits an error indication to the memory device in response to the error-detection code. The error indication causes the memory device to remove the received address and prevent a memory operation

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 14/020,755, filed for “Memory Error Detection” on behalf of inventors Ian Shaeffer and Craig E. Hampel on Sep. 6, 2013, which in turn is a continuation of U.S. patent application Ser. No. 13/666,918, filed for “Memory Error Detection” on behalf of inventors Ian Shaeffer and Craig E. Hampel on Nov. 1, 2012 (now U.S. Pat. No. 8,555,116), which in turn is a continuation of U.S. patent application Ser. No. 12/424,094 (now U.S. Pat. No. 8,352,805), filed for “Memory Error Detection” on behalf of inventors Ian Shaeffer and Craig E. Hampel on Apr. 15, 2009, which in turn is a continuation-in-part application of U.S. patent application Ser. No. 12/035,022 (now U.S. Pat. No. 7,836,378), filed for “System to Detect and Identify Errors in Control Information, Read Data and/or Write Data” on behalf of inventors Ian Shaeffer, Craig Hampel, Yuanlong Wang, and Fred Ware on Feb. 21, 2008, which in turn is a continuation of U.S. patent application Ser. No. 11/436,284, filed for “System to Detect and Identify Errors in Control Information, Read Data and/or Write Data” on behalf of inventors Ian Shaeffer and Craig Hampel. U.S. patent application Ser. Nos. 14/020,755, 13/666,918 and 12/424,094 are hereby incorporated by reference as though set forth herein.

BACKGROUND

The present disclosure relates generally to memory systems. More particularly, the present disclosure relates to detection and correction of errors within a memory system.

As the data transfer rate in computer systems becomes progressively faster, modern memory systems are more prone to transmission errors. Noise, crosstalk, inter-symbol interference, among other factors, can significantly impair signal quality, especially as data rates approach multiple Gbps.

BRIEF DESCRIPTION OF THE FIGURES

This disclosure is illustrated by way of example, and not by way of limitation, in the accompanying drawings. Like reference numerals refer to similar elements.

FIG. 1 illustrates an exemplary memory system which facilitates error detection for both data and address, in accordance with one embodiment of the present invention.

FIG. 2A presents a block diagram illustrating the process of generating EDC codes based on both data and address, in accordance with one embodiment of the present invention.

FIG. 2B presents a block diagram illustrating the process of generating EDC codes based on both data and address, in accordance with one embodiment of the present invention.

FIG. 3 presents a flowchart illustrating the operation of a dynamic random-access memory (DRAM) which facilitates EDC for both address and data, in accordance with one embodiment of the present invention.

FIG. 4 presents a flowchart illustrating the operation of a memory controller which facilitates EDC for both address and data, in accordance with one embodiment of the present invention.

FIG. 5 presents an exemplary timing diagram illustrating the operation between a memory controller and a DRAM to facilitate address and data EDC, in accordance with one embodiment of the present invention.

FIG. 6 presents an exemplary timing diagram illustrating the operation between a memory controller and a DRAM to facilitate address and data EDC, in accordance with one embodiment of the present invention.

The following description is presented to enable any person skilled in the art to make and use embodiments disclosed herein, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the present disclosure is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the disclosure.

DETAILED DESCRIPTION

In a memory system, address errors can be more detrimental than data errors, because a write operation with the wrong address can corrupt previously stored data. Embodiments of the present invention provide a mechanism for checking and correcting errors in both address and data transmission between the memory controller and DRAM. The DRAM computes an error-detection code (EDC) based on the address and/or data received from the controller, and transmits this EDC code back to the controller. The controller then determines whether the EDC code is consistent with the previously transmitted address and/or data. If an error is detected, and if the error corresponds to the address for a write operation, the controller can send an error indication to the DRAM, so that the DRAM can cancel the erroneous write command. In this way, the memory system can ensure both error-resistant data and address transmission.

Embodiments of the present invention also provide various configurations to optimize different characteristics of the memory system. For example, the DRAM can compute the address-based EDC code as soon as the address is received, thereby reducing the amount of latency incurred to the data due to buffering. The DRAM also subjects the received address (and optionally the received data) to additional delays, so that there is sufficient time for the controller to detect an error based the EDC code and issue an error indication. The total delay incurred to the address and optionally the data is sufficient such that the operation corresponding to an erroneous address can be precluded from being completed. This total delay may be more than the normal WRITE or READ latency. In further embodiments, the controller can withhold the data transmission until it receives and confirms the EDC code for the corresponding address, which reduces the amount of in-DRAM data buffering.

In the present disclosure, a “memory controller” or “controller” refers to a circuit, chip, or device on a computer's motherboard or CPU die which manages the flow of data going to and from the memory. A “DRAM” refers a dynamic random-access memory. Embodiments of the present invention are not limited to DRAM-specific applications. These embodiments can also be applied to various memory systems based on dynamic or static memories. The terms “data transmission” and “data” refer to the payload data transferred between the controller and DRAM. Although the address and command bits can also be broadly referred to as data, the term “data” in this disclosure, unless specified otherwise, refers to the payload bits which are separate from address and command bits. An “error indication” is a command or a signal transmitted by the controller to a DRAM, so the DRAM can prevent a memory operation corresponding to an erroneously received address from being completed. An error indication can be a command including one or more bits, transmitted via or outside of the command bus. The error indication can also be a separate signal transmitted via one or more separate pins.

FIG. 1 illustrates an exemplary memory system 100 which facilitates error checking and correction for both data and address, in accordance with one embodiment of the present invention. Memory system 100 includes a DRAM controller 110, a DRAM 140, a command bus 132, an address bus 134, a data bus (DQ bus) 136, and an error-detection code (EDC) bus 138. DRAM controller 110 includes command generation circuitry 113, address generation circuitry 112, write data circuitry 114, read data circuitry 116, a write data buffer 122, an address buffer 124, a read/write selector 120, and error detection circuitry 118. DRAM 140 includes command/error handling circuitry 142, an address buffer 146, a data buffer 147, a read/write selector 148, and a cyclic-redundancy-check (CRC) code generator 150.

During operation, command generation circuitry 113 generates a memory command, e.g., a read or write command, and places the command on command bus 132. At approximately the same time, address generation circuitry 112 places an address corresponding to the memory command on address bus 134. If the command is for a write operation, write data circuitry 114 places the data for the write operation in buffer 122. In general, buffer 122 is used to delay the data transmission after the write command and address have been sent to DRAM 140, due to the write latency present in DRAM 140, i.e., the delay between the time when DRAM 140 receives the command and address and the time when DRAM 140 is ready to accept data on DQ bus 136. If command generation circuitry 113 generates a read command, a certain amount of data buffering might also be necessary to accommodate the read latency in DRAM 140.

After command generation circuitry 113 places the command on command bus 132, command/error handling circuitry 142 in DRAM 140 receives the transmitted command. In addition, the corresponding address is received and placed in buffer 146. Typically, buffer 146 buffers the received address bits because the complete address (e.g., bank address, row address, and/or column address) may be transmitted over multiple clock cycles. Furthermore, buffer 146 ensures that the address information remains available until DRAM 140 is ready to receive the write data.

Subsequently, after a certain delay (e.g., the write latency), the corresponding data is received and buffered in buffer 147. Buffer 147 buffers the received data so that buffer 147 can be later frozen or the data can be discarded if DRAM controller 110 identifies an error in the transmitted address. At a given time, the data present on DQ bus 136 might not correspond to the address and/or command present on address bus 134 and command bus 132, due to the pipelined operation of memory system 100.

The received address is first buffered by buffer 146 and then sent to CRC generator 150. In addition, the write data is sent to CRC generator 150 via read/write selector 148. Read/write selector 148 is controlled by command/error handling circuitry 142 based on the received command. If the command indicates a read operation, read/write selector 148 allows the outgoing data from the DRAM core to be sent to CRC generator 150. If the command indicates a write operation (which is the case in the current example), read/write selector 148 allows the write data to be sent to CRC generator 150.

CRC generator 150 produces a CRC code based on both the address and write data. The CRC code is then transmitted via EDC bus 138 to DRAM controller 110. CRC generator 150 can concatenate the address with the data to produce an input to the CRC computation. Other methods of generating the CRC code based on both the address and data are also possible.

In this example, the EDC code generated by DRAM 140 is a CRC code. A CRC code (or “CRC”) is an error-detecting code. Its computation resembles a long division operation in which the quotient is discarded and the remainder becomes the result, with the distinction that the arithmetic used is the carry-less arithmetic of a finite field. The length of the remainder is less than or equal to the length of the divisor, which therefore determines how long the result can be. The definition of a particular CRC specifies the divisor to be used. The CRC code generated by CRC generation circuitry 150 can be based on the polynomial expression X⁸+X²+X¹+1. In general, a respective EDC pin in EDC bus 138 is used to carry the CRC code for the data transmitted on a number (e.g., eight) of DQ pins within DQ bus 136. There is one EDC pin for every eight DQ pins, and the CRC code is transmitted via the EDC pin over eight data-clock periods, which correspond to eight data bits transmitted over each DQ pin. That is, an eight-bit serial CRC code is transmitted over one EDC pin for 64 bits of data transmitted via eight DQ pins over eight data-clock cycles. Other EDC code schemes can also be used.

After DRAM controller 110 receives the CRC code, error detection circuitry 118 compares the CRC code with a local CRC code generated based on the buffered write data and address. Alternatively, error detection circuitry 118 can checksum the buffered write data and address concatenated with the same CRC polynomial, and determines whether the checksum result is zero. The write address is buffered in buffer 124 to compensate for the delay between the time when the address is transmitted to DRAM 140 and the time when the CRC code is received and checked at DRAM controller 110. Error detection circuitry 118 also takes as input the write or read data which corresponds to the CRC received from DRAM 140. Controller 110 maintains a set of state information to keep track of the address and data (which may be for different memory operations) corresponding to the received CRC code. The state information may be maintained by command generation circuitry 113. Upon receiving the CRC code from DRAM 140, command generation circuitry 113 determines whether the received CRC code corresponds to write or read data, and sends a signal (denoted as “R/W”) to read/write selector 120. In response, read/write selector 120 selects the appropriate data (i.e., write or read) to send to error detection circuitry 118.

If the received CRC code is consistent with the selected data and address, controller 110 does not send any error indication to DRAM 140. As a result, after a predetermined period, DRAM 140 can automatically proceed with the write operation based on the address stored in buffer 146 and the corresponding write data.

Instead of transmitting an explicit error indication, controller 110 can transmit an explicit “commit” indication to DRAM 140 when the CRC code is consistent with the buffered data and address. This commit indication can be a command transmitted via or outside the command bus, or a signal transmitted over one or more separate pins. In response to the commit indication, DRAM 140 can proceed to commit the memory operation to the DRAM core. If the CRC code is inconsistent with the buffered data and address at controller 110, no commit indication is sent. As a result, after a certain time-out period, DRAM 140 can prevent the memory operation from being completed if no commit indication is received.

If error detection circuitry 118 detects an error based on the received CRC code, it can cause command generation circuitry 113 to generate and transmit an error indication to DRAM 140 via command bus 132. (The error indication can also be transmitted via one or more dedicated pins separate from command bus 132.) In response, command/error handling circuitry 142 can cause buffer 146 to remove the stored address corresponding to the error, and optionally cause buffer 147 to remove the corresponding write data. Buffer 146 can include a number of latches, and removing the stored address involves resetting these latches. In addition, in response to the error indication, command/error handling circuitry 142 can prevent the memory operation corresponding to the erroneously received address from being completed. For example, a commit of the memory operation to the memory core can be deliberately delayed sufficiently long using buffer 146 and/or buffer 147, such that controller 110 has time to detect errors and, if appropriate, abort the associated command. Subsequently, command generation circuitry 113 re-issues the corresponding memory commands. It is possible that the CRC code which identifies an error is derived from a write address and read data. In this case, the controller does not need to determine the source of the error (i.e., whether the error was incurred to the write address or read data) and can simply re-transmit all the transactions to which the erroneous CRC code corresponds.

Depending on the pipelined operations, DRAM 140 may discard a number of “in-flight” transactions (including command, address, and optionally data) received after the memory operation corresponding to the erroneous address. This approach can avoid read-after-write and write-after-write conflicts that could otherwise occur and also corrupt data in some way. In general, command/error handling circuitry 142 can discard the memory command associated with the error (or commands associated with the error if the error corresponds to more than one command due to pipelining). Command/error handling circuitry 142 can further discard any subsequently received command that can present a hazardous conflict with the command in error (for example, a read-after-write or write-after-read situation). Alternatively, command/error handling circuitry 142 can discard all the commands it has received and buffered after the erroneous command and before the first retransmitted command.

The CRC code could be generated based on address and data which belong to two or more memory operations due to the pipelined operation between controller 110 and DRAM 140. As a result, command generation circuitry 113 may need to re-issue two memory commands. Furthermore, if a write command is re-issued, the write data previously buffered in buffer 122 is sent to DRAM 140 again, in response to a signal from error detection circuitry 118 (denoted by an arrow from error detection circuitry 118 to buffer 122).

To minimize the delay between address transmission and the receiving of CRC code at controller 110, DRAM 140 can be configured to compute the CRC code as soon as the address is received, without first buffering the received address (denoted by a dotted arrow from the address flow to CRC generator 150). The CRC code can also be generated based on the address and data bits for the same memory operation. This configuration may involve additional buffering of the address, because the data transmission typically occurs after the address transmission. It is, nevertheless, not required to generate the CRC code based on the address and data corresponding to the same memory transaction, so long as both the controller and DRAM have an agreement on how to map a CRC code to the appropriate memory transaction(s).

Controller 110 can withhold the write data transmission until a CRC code corresponding to the address for the same operation is received and confirmed. This configuration may require additional buffering of the write data within controller 110. This buffering can be accomplished by buffer 122.

The example described above is described in the context of a write operation. In the case of a read operation, read/write selector 148 allows the data read from the DRAM core to be sent to CRC generator 150. In controller 110, read/write selector 120 also allows the received read data to be sent to error detection circuitry 118. If an error is detected for a read command, only the read command and the corresponding address is re-transmitted to DRAM 140, since errors in a read command, address, or data do not potentially result in irrecoverable data corruption in DRAM 140.

As noted above, there is usually write and read latency within DRAM 140. To improve system efficiency and utilization, the transfer of addresses and data between controller 110 and DRAM 140 is typically pipelined. That is, at a given moment, the bits carried on address bus 134 and the bits carried on data bus 136 may correspond to different operations. Hence, CRC generator 150 can generate CRC codes based on address and data belonging to different operations.

FIG. 2A presents a block diagram illustrating the process of generating a CRC code with pipelined write operations, in accordance with one embodiment of the present invention. This example shows a number of write operations, the address and data of which (denoted as “A” and “D” respectively) are indexed by a subscript which indicates their order. These write operations are pipelined in such a way that the write data for a prior operation can be present on the DQ bus when the address for the current operation is on the address bus. In FIG. 2A, the write data is assumed to lag behind the address by k memory commands. For example, when address A_(n) is on the address bus, write data D_(n−k) is on the DQ bus. As a result, the CRC generator within the DRAM can generate a CRC code, CRC_(n), based on A_(n) and D_(n−k). k can be any integer, such as 0, 1, 2, 3, etc.

The value of k represent the about of lag of data behind the corresponding address. In addition to the write or read latency inherent in the DRAM, k can also include artificially injected buffering delay to the data to accommodate the time required to generate the CRC code, process the CRC code at the controller, and to issue an error indication by the controller. This way, the buffered memory command can be aborted before the data is committed to the DRAM core.

When k is zero, the data on the DQ bus is substantially aligned with the address on the address bus and they correspond to the same memory operation. However, in such a configuration, the DRAM may need to provide sufficient in-DRAM buffering for the write data to accommodate the write latency. One advantage of having the data and address aligned (i.e., corresponding to the same memory command) for generating the CRC code is that when an error is detected, the DRAM only needs to abort and/or re-issue the memory command corresponding to that error. When the data and address are not aligned (i.e., k is greater than zero), the controller might not be able to determine whether the error in the CRC corresponds to the data or address. As a result, the DRAM might need to abort multiple commands corresponding to the address and data, respectively. The controller might also need to re-issue these commands.

It is possible that sometimes the DQ bus is not always busy, and a given CRC code might be generated based only on an address, whereas the data portion of the input for the CRC is of a null value. In this case, the DRAM only needs to abort the command corresponding to the address if an error is detected in the CRC code.

In the example in FIG. 2B, a CRC code, CRC_(n), is generated based on A_(n), D_(n−k), and D_(n−k+1). In other words, a particular CRC is generated based on not only the address and data present on the address bus and DQ bus, but also on the data corresponding to the previous memory command. This method can allow the controller to determine whether an error in CRC_(n) is caused by an error in A_(n), D_(n−k), or D_(n−k+1). For example, if CRC_(n) is in error, but CRC_(n+1) and CRC_(n−1) are both correct, then A_(n) is in error. If CRC_(n) and CRC_(n−1) are both in error but CRC_(n+1) and CRC_(n−1) are correct, then it is possible that D_(n−k) and/or A_(n) are in error.

Other methods are possible to allow the controller to determine whether a CRC error is caused by an address error or data error. For example, the DRAM can generate CRC codes for the data and address separately, and transmit both CRC codes to the controller.

The description below provides further explanation of the operations of the DRAM and controller, and exemplary timing diagrams of different embodiments.

FIG. 3 presents a flowchart illustrating the operation of a DRAM which facilitates EDC for both address and data, in accordance with one embodiment of the present invention. In this example, the DRAM first receives a command and the corresponding address (operation 302). The DRAM can also receive write data if the command is for a write operation, wherein the write data may or may not correspond to the write command and address due to pipelined operations. Subsequently, the DRAM computes a CRC code based on the received address and optionally the data (operation 304). The data could be write data (incoming) or read data (outgoing). The DRAM then transmits the CRC code to the memory controller (operation 306).

Next, the DRAM determines whether it has received an error indication from the controller before a given time (referred to as “retire time”) (operation 308). If the DRAM does not receive the error indication before the retire time, the DRAM proceeds with normal operations, such as write, read, active, refresh, and other register-related operations (operation 310). If an error indication is received, the DRAM purges the address corresponding to the error from the address buffer and optionally one or more pending commands following the command in error (operation 314). Subsequently, the DRAM receives a re-issued write or read command, the address, and optionally data (if the re-issued command is for a write operation) from the controller (operation 316). The DRAM then proceeds to handle the re-issued command (operation 304).

FIG. 4 presents a flowchart illustrating the operation of a memory controller which facilitates EDC for both address and data, in accordance with one embodiment of the present invention. In this example, the memory controller first transmits a command and address, and optionally write data to the DRAM (operation 402). Subsequently, the controller receives from the DRAM a CRC code based on the transmitted address and optionally write or read data (operation 404). The controller then performs the checksum computation on the buffered address (and optionally buffered data) concatenated with the received CRC code (operation 406). A correct CRC code would produce zero as the checksum result. Alternatively, the controller can generate its own CRC code and compare it with the received CRC code. The address and optionally the data and command used to generate the CRC code should be the same as the ones used to check the CRC code. However, they do not need to be for the same memory transaction.

Next, the controller determines whether received CRC code is correct (operation 408). If the CRC codes is correct, the controller proceeds to the next memory operation (operation 410). If the CRC code is incorrect, the controller further determines whether the address associated with the error corresponds to a read or write operation (operation 412).

If the address error corresponds to a write operation, the controller issues an error indication to the DRAM (operation 414). This error indication notifies the DRAM that it should discard or abort the commands for the previously stored erroneous address, and, if the corresponding write data has already been transmitted to the DRAM, discard the buffered write data as well. Subsequently, the controller re-issues the write command corresponding to the erroneous address (operation 416). Optionally, if the CRC code from the DRAM is based on address and data belonging to two different memory operations, the controller can re-issue the write or read command corresponding to the data portion (as opposed to the address portion) associated with the error (operation 420).

In a further embodiment, instead of sending an explicit error indication to the DRAM when the CRC is incorrect, the controller can send an explicit commit indication when the CRC is correct. This commit indication allows the DRAM to proceed with the buffered command and complete the memory operation. Correspondingly, if the CRC is incorrect, the controller does not transmit the commit indication, and the DRAM discards the command in error (and optionally additional pending commands received after the command in error) after a predetermined time-out period.

If the erroneous data portion is for a previously issued write command, it is not necessary for the controller to issue an error indication to the DRAM to discard the erroneous data, because the erroneous data will still be written to the correct address and will not corrupt good data stored elsewhere. The controller only needs to re-issue the write command to place the correct data in the same address. To illustrate this situation more clearly, take the example in FIG. 2. Suppose address A_(n) and data D_(n−k) are for two separate write commands. Also, suppose CRC_(n) indicates an error. The controller then assumes that both write commands respectively corresponding to A_(n) and D_(n−k) had erroneous transmission. However, the controller only needs to issue an error indication for the write operation corresponding to A_(n), so that the DRAM can purge the stored erroneous address A_(n)′. The controller does not have to issue an error indication for the write operation corresponding to D_(n−k), because even if the erroneous data is written to the DRAM core, it can be corrected by a re-issued write command, since there is no address error associated with D_(n−k). This is based on the assumption that the controller does not issue a read command immediately following the erroneous write command to the same address. The controller can ensure this does not happen by comparing the address of pending read operations with the erroneous write operation and holding the read operations until the correct write data is committed. Alternatively, the controller can return the correct read data based on the data buffered within the controller, without addressing the DRAM at all.

Now, with reference back to operation 412 in FIG. 4, if the controller determines that the address associated with the error corresponds to a read operation, the controller re-issues the read command corresponding to the erroneous address (operation 418). The controller can optionally re-issue the write or read command corresponding to the data portion associated with the error (operation 420). Subsequently, the controller proceeds to receive the next CRC code from the DRAM (operation 404).

Note that although the above example is directed to erroneous read and write operations, the same method can be applied to other types of operations, such as activate, refresh, and other register-related operations. In general, this method can be applied to any memory operation that involves transmission of an address.

FIG. 5 presents an exemplary timing diagram illustrating the operation between a memory controller and a DRAM to facilitate address and data EDC, in accordance with one embodiment of the present invention. In this example, the clock and inverted clock signals are denoted as “clk” and “ clk” respectively. Each clock cycle is denoted as T_(i). The command can be transmitted at every rising edge of clk, and address can be transmitted at every rising edge of clk and clk. In other words, the data rate of address transmission is twice that of command transmission. The data clock used in this example is twice as fast as the clock for command and address transmission. Here, the data clock and inverted data clock signals are denoted as “wclk” and “ wclk” respectively. The data bits on the DQ bus and the CRC bits on the EDC bus are transmitted at every rising edge of wclk and wclk. Hence, the data rate of DQ and EDC is four times the data rate of the command bus and twice the data rate of the address bus.

In this example, at clock cycle T₀, the controller issues a write command WR₀, and places the corresponding addresses, AD₀₁ and AD₀₂, on the address bus. Assume that the DRAM has a write latency of two clock cycles (i.e., WL=2). The corresponding write data burst 512 is placed on the DQ bus at clock cycle T₂. Assume that each write data burst is eight bits long. Hence, data burst 512 occupies clock cycles T₂ and T₃. Meanwhile, at T₃, the controller issues the next write command WR₁ and the corresponding addresses AD₁₁ and AD₁₂. AD₁₁ and AD₁₂ are received by the DRAM at approximately the same time as data burst 512 (which is the write data for WR₀). The DRAM concatenates AD₁₁ and AD₁₂ with data burst 512, generates a CRC code 522, and places CRC code 522 on the EDC bus at T₄.

While the controller receives CRC code 522, the controller continues to issue the next write command, WR₂, and its corresponding address AD₂₁ and AD₂₂ at T₅. In addition, at T₅, the controller places data burst 514, which is the write data for WR₁, on the DQ bus.

After receiving CRC code 522, the controller detects an error (indicated by a star), and issues an error indication 515 to the DRAM at T₇. Error indication 515 corresponds to the write command WR₁ and allows the DRAM to discard the erroneously received addresses AD₁₁ and AD₁₂. Subsequent to error indication 515, the controller re-issues WR₀ and WR₁ at T₈ and T₁₀, respectively. The controller does not need to issue an error indication for WR₀, if the address of WR₀ has been received correctly by the DRAM and there is no potential data hazard between WR₀ and WR₁. In response to error indication 515, the DRAM can discard the buffered address AD₀₁ and AD₀₂, and optionally buffered data burst 512.

Meanwhile, at T₇, the controller places data burst 516, which is the write data corresponding to WR₂, on the DQ bus. On the DRAM side, after receiving data burst 514, the DRAM concatenates AD₂₁ and AD₂₂ with data burst 514 and generates CRC code 524. Subsequent to data burst 514, the controller transmits data burst 516, which is the write data for WR₂. At T₁₀, the controller transmits data burst 518, which is the write data for the re-issued WR₀.

Because data bursts 514 and 516 are received at the DRAM back-to-back, the DRAM also generates CRC code 526 based on AD₀₁, AD₀₂, and data burst 516. AD₀₁ and AD₀₂ at T₈ correspond to the re-issued WR₀. Since the controller does not find any error in CRC codes 524 and 526 (indicated by a check mark), the controller does not perform any additional operations with respect to these CRC codes.

In this example, there are seven clock cycles between the time when the address for WR₀ (AD₀₁ and AD₀₂) is placed on the address bus and the time when error indication 515 is issued. Correspondingly, these addresses are buffered in the DRAM for seven clock cycles in order for the DRAM to abort them in response to an error indication. This buffer delay is longer than the DRAM's normal write latency, which is two clock cycles. This buffering can be provided by buffer 146 in the system illustrated in FIG. 1. If the time required for the DRAM to compute the CRC and for the controller to check the CRC and issue an error indication is deterministic, the amount of buffering for the received address can also be determined. Furthermore, the DRAM can include a mechanism that determines this total latency required for the CRC check and configure the buffer automatically during a start-up sequence, such that the received addresses are buffered sufficiently long to allow the CRC check and error notification.

FIG. 6 presents an exemplary timing diagram illustrating the operation between a memory controller and a DRAM to facilitate address and data EDC, in accordance with one embodiment of the present invention. In this example, the controller is configured to transmit the write data after the corresponding write address is confirmed to have been received successfully at the DRAM. The write latency in this example is assumed to be three clock cycles (i.e., WL=3).

As illustrated in FIG. 6, at T₀, the controller issues the first write command WR₀ and the corresponding addresses, AD₀₁ and AD₀₂. Based on AD₀₁ and AD₀₂, the DRAM generates CRC code 622. Subsequently, the controller determines that CRC code 622 is error-free, and transmits data burst 614, which is the write data for WR₀. Similarly, the DRAM generates CRC code 624 based on AD₁₁ and AD₁₂. Upon receiving and confirming CRC code 624, the controller transmits data burst 616, which is the write data corresponding to WR₁.

Data burst 614 is transmitted at T₃. Since data burst 614 lasts two full clock cycles (i.e., from T₃ to T₅), which coincide with the transmission of WR₂, AD₂₁, and AD₂₂, the DRAM can first buffer AD₂₁ and AD₂₂ and then concatenate them with data burst 614 to produce CRC code 626. Upon receiving and confirming CRC code 626, the controller proceeds to transmit data burst 618, which is the write data corresponding to WR₂.

In the example above, the DRAM generates a CRC code based on the received address as soon as the address is received, provided there is no data being received on the DQ bus. The controller would withhold the write data transmission until the CRC code corresponding to the write address is received and confirmed. However, when the DRAM receives addresses and data at the same time (for example, data burst 614, AD₂₁, and AD₂₂), the DRAM can first buffer the address and then generate the CRC code based on both the address and received data.

Although the description uses read and write operations as examples, the methods disclosed herein are not limited to these operations. In general, the present address error-detection mechanisms are applicable with any memory operation that involves an address transmission.

The components of the address error detection mechanism described above can include any collection of computing components and devices operating together. These components can also be components or subsystems in a larger computer system or network. Components of an address error detection mechanism can also be coupled among any number of components (not shown), for example, buses, controllers, memory devices, and data input/output (I/O) devices, in any number of combinations. Many of these system components may be situated on a common printed circuit board or integrated circuit, or may be integrated in a system that includes several printed circuit boards or ICs that are coupled together in a system, for example, using connector and socket interfaces such as those employed by personal computer motherboards and dual inline memory modules (“DIMM”). In other examples, complete systems may be integrated in a single package housing a system in package (“SIP”) type of approach. Integrated circuit devices may be stacked on top of one another and utilize wire bond connections to effectuate communication between devices or may be integrated on a single planar substrate in the package housing.

Further, functions of an address error detection mechanism can be distributed among any number/combination of other processor-based components. The address error detection mechanism described above can be applied in, for example, various DRAM systems. As examples, the DRAM memory systems can include DDR systems like DDR SDRAM, as well as DDR2 SDRAM, DDR3 SDRAM, and other DDR SDRAM variants, such as Graphics DDR (“GDDR”) and further generations of these memory technologies, including GDDR2, GDDR3, GDDR4, and GDDR5, but are not limited to these memory systems.

Aspects of the address error detection mechanisms described herein may be implemented as functionality programmed into any of a variety of circuitry, including programmable logic devices (PLDs), such as field programmable gate arrays (FPGAs), programmable array logic (PAL) devices, electrically programmable logic and memory devices, and standard cell-based devices, as well as application specific integrated circuits (ASICs). The underlying device technologies may be provided in a variety of component types, e.g., metal-oxide semiconductor field-effect transistor (MOSFET) technologies like complementary metal-oxide semiconductor (CMOS), bipolar technologies like emitter-coupled logic (ECL), polymer technologies (e.g., silicon-conjugated polymer and metal-conjugated polymer-metal structures), mixed analog and digital, etc.

The foregoing descriptions of embodiments described herein have been presented only for purposes of illustration and description. They are not intended to be exhaustive or to limit the embodiments to the forms disclosed. Accordingly, many modifications and variations will be apparent to practitioners skilled in the art.

Moreover, some components are shown directly connected to one another, while others are shown connected via intermediate components. In each instance the method of interconnection, or ‘coupling,’ establishes some desired electrical communication between two or more circuit nodes, or terminals. Such coupling may often be accomplished using a number of circuit configurations, as will be understood by those of skill in the art. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description. Only those claims specifically reciting “means for” or “step for” should be construed in the manner required under the sixth paragraph of 35 U.S.C. §112. 

We claim:
 1. A dynamic random access memory (DRAM) integrated circuit, comprising: circuitry to receive, from a memory controller, an address with a write command that specifies a write operation; circuitry to buffer the write command for an interval of time comprising a latency associated with time to perform the write operation and an interval of time associated with detection of an error in the address; and circuitry to cause the DRAM integrated circuit to preclude the write operation from being completed if an error is determined to exist in the address within the interval of time and to complete the write operation following expiration of the latency in absence of a determination that there is an error associated with the write command.
 2. The DRAM integrated circuit of claim 1, wherein the interval of time and the latency are each expressed as an integer number of clock cycles.
 3. The DRAM integrated circuit of claim 2, wherein DRAM integrated circuit includes circuitry programmable by the memory controller during a start-up sequence to define the interval of time.
 4. The DRAM integrated circuit of claim 2, wherein said DRAM integrated circuit comprises circuitry to determine the interval of time during the start-up sequence.
 5. The DRAM integrated circuit of claim 1, wherein the DRAM integrated circuit is also to receive, from the memory controller, a read address with a read command that specifies a read operation, and wherein circuitry of the DRAM integrated circuit is to buffer the read command for an interval of time comprising a latency associated with time to perform the read operation and an interval of time associated with detection of an error in the read address.
 6. The DRAM integrated circuit of claim 1, wherein the DRAM integrated circuit is to send information to the memory controller and the memory controller is to determine whether there is an error in the address.
 7. The DRAM integrated circuit of claim 6, wherein: the information comprises an error detection code; the DRAM integrated circuit comprises circuitry to calculate the error detection code; and the circuitry to cause the DRAM integrated circuit to preclude the write operation from being completed if an error is determined to exist in the address within the interval of time, and to complete the write operation following expiration of the latency in absence of a determination that there is an error associated with the command, comprises circuitry to remove the write command from a queue resident in the DRAM integrated circuit responsive to an abort command from the memory controller.
 8. The DRAM integrated circuit of claim 1, wherein the DRAM integrated circuit is to permit completion of the write operation notwithstanding error confined to write data associated with the write command.
 9. The DRAM integrated circuit of claim 1, wherein the DRAM integrated circuit further comprises circuitry to notify the memory controller responsive to error in write data associated with the write command.
 10. The DRAM integrated circuit of claim 1, wherein: the DRAM integrated circuit further comprises a queue to store at least one command from the memory controller subsequent to the write command; the circuitry to cause the DRAM integrated circuit to preclude the write operation from being completed if an error is determined to exist in the address within the interval of time, and to complete the write operation following expiration of the latency in absence of a determination that there is an error associated with the command further comprises circuitry to discard from the queue a command of the at least one command from the memory controller subsequent to the write command if an error is determined to exist in the address within the interval of time; and the DRAM integrated circuit is thereby operable to abort multiple commands, including the write command, if an error is determined to exist within the address within the interval of time.
 11. A dynamic random access memory (DRAM) integrated circuit, comprising: circuitry to receive, from a memory controller, an address with a write command that specifies a write operation; circuitry to buffer the write command for an interval of time comprising a latency associated with time to perform the write operation and a buffering delay associated with additional time associated with detection of an error in the address; circuitry to cause the DRAM integrated circuit to preclude the write operation from being completed if an error is determined to exist in the address within the interval of time and to complete the write operation following expiration of the latency in absence of a determination that there is an error associated with the command; and circuitry programmable by the memory controller to store a value, the interval of time being dependent on the value.
 12. The DRAM integrated circuit of claim 11, wherein the interval of time is defined as an integer number of clock cycles.
 13. The DRAM integrated circuit of claim 11, wherein the DRAM integrated circuit is also to receive, from the memory controller, a read address with a read command that specifies a read operation, and wherein circuitry of the DRAM integrated circuit is also to buffer the read command for an interval of time comprising a latency associated with time to perform the read operation and an artificially injected buffering delay associated with time associated with detection of an error in the read address.
 14. The DRAM integrated circuit of claim 11, wherein the DRAM integrated circuit is to send information to the memory controller and the memory controller is to determine whether there is an error in the address.
 15. The DRAM integrated circuit of claim 14, wherein: the information comprises an error detection code; the DRAM integrated circuit comprises circuitry to calculate the error detection code; and the circuitry to cause the DRAM integrated circuit to preclude the write operation from being completed if an error is determined to exist in the address within the interval of time, and to complete the write operation following expiration of the latency in absence of a determination that there is an error associated with the command, comprises circuitry to remove the write command from a queue resident in the DRAM integrated circuit responsive to an abort command from the memory controller.
 16. The DRAM integrated circuit of claim 11, wherein the DRAM integrated circuit is to permit execution of the write command notwithstanding error confined to write data associated with the write command.
 17. The DRAM integrated circuit of claim 11, wherein the DRAM integrated circuit further comprises circuitry to notify the memory controller responsive to error in write data associated with the write command.
 18. The DRAM integrated circuit of claim 11, wherein: the DRAM integrated circuit further comprises a queue to store at least one command from the memory controller subsequent to the write command; the circuitry to cause the DRAM integrated circuit to preclude the write operation from being completed if an error is determined to exist in the address within the interval of time, and to complete the write operation following expiration of the latency in absence of a determination that there is an error associated with the command further comprises circuitry to discard from the queue a command of the at least one command from the memory controller subsequent to the write command if an error is determined to exist in the address within the interval of time; and the DRAM integrated circuit is thereby operable to abort multiple commands, including the write command, if an error is determined to exist within the address within the interval of time.
 19. A dynamic random access memory (DRAM) integrated circuit, comprising: circuitry to receive, from a memory controller, an address with a write command that specifies a write operation; a queue to store at least one command from the memory controller subsequent to the write command; circuitry to buffer the write command for a number of clock cycles comprising a latency associated with time needed to perform the write operation and an interval of time associated with detection of an error in the address; and circuitry to cause the DRAM integrated circuit to preclude the write operation from being completed if an error is determined to exist in the address within the number of clock cycles and to complete the write operation following expiration of the latency in absence of a determination that there is an error associated with the command, including circuitry to discard from the queue a command of the at least one command from the memory controller subsequent to the write command if an error is determined to exist in the address within the number of clock cycles.
 20. The DRAM integrated circuit of claim 19, wherein the DRAM integrated circuit is to permit completion of the write operation notwithstanding error confined to write data associated with the write command. 